The present invention relates to a system and method for the treatment of disorders of the vasculature. More specifically, the present invention relates to a system and method for treatment of abdominal aortic aneurysm and the like, which is a condition manifested by expansion and weakening of the aorta below the diaphragm. Such conditions require Intervention due to the severity of the sequelae, which frequently is death. Prior methods of treating aortic aneurysm have consisted of invasive surgical methods with graft placement within the aorta as a reinforcing member of the artery. However, such a procedure requires a surgical cut down to access the vessel, which in turn can result in a catastrophic rupture of the aneurysm due to the decreased external pressure from the organs and tissues surrounding the aorta, which are moved during the procedure to gain access to the vessel. Accordingly, surgical procedures have a high mortality rate due to the possibility of the rupture discussed above in addition to other factors. Such other factors can include poor physical condition of the patient due to blood loss, anuria, and low blood pressure associated with the aortic abdominal aneurysm. An example of a surgical procedure is described in a book entitled Surgical Treatment of Aortic Aneurysms by Denton A. Cooley, M.D., published in 1986 by W. B. Saunders Company.
Due to the inherent risks and complexities of surgical procedures, various attempts have been made In the development of alternative methods for deployment of grafts within aortic aneurysms. One such method is the non-invasive technique of percutaneous delivery by a catheter-based system. Such a method is described in Lawrence, Jr. et al in xe2x80x9cPercutaneous Endovascular Graft: Experimental Evaluationxe2x80x9d, Radiology (May 1987). Lawrence described therein the use of a Gianturco stent as disclosed in U.S. Pat. No. 4,580,568. The stent is used to position a Dacron fabric graft within the vessel. The Dacron graft is compressed within the catheter and then deployed within the vessel to be treated. A similar procedure has also been described by Mirich et at in xe2x80x9cPercutaneously Placed Endovascular Grafts for Aortic Aneurysms: Feasibility Studyxe2x80x9d, Radiology (March 1989). Mirich describes therein a self-expanding metallic structure covered by a nylon fabric, with said structure being anchored by barbs at the proximal and distal ends.
One of the primary deficiencies of the existing percutaneous devices and methods has been that the grafts and the delivery catheters used to deliver the grafts are relatively large in profile, often up to 24 French and greater, and stiff in bending. The large profile and bending stiffness makes delivery through the irregular and tortuous arteries of diseased vessels difficult and risky. In particular. the iliac arteries are often too narrow or irregular for the passage of a percutaneous device. Because of this, non-invasive percutaneous graft delivery for treatment of aortic aneurysm is not available to many patients who would otherwise benefit from it.
Another contraindication for current percutaneous grafting methods and devices is a vessel treatment site with high neck angulation which precludes a proper fit between the graft and the vessel wall. An improper fit or seal between the graft and the vessel wall can result in leaks or areas of high stress imposed upon the diseased vessel which lead to reduced graft efficacy and possibly rupture of the aneurysm.
While the above methods have shown some promise with regard to treating abdominal aortic aneurysms with non-invasive methods, there remains a need for an endovascular graft system which can be deployed percutaneously in a small diameter flexible catheter system. In addition, there is a need for a graft which conforms more closely to the contours of an aortic aneurysm which are often quite irregular and angulated and vary from patient to patient. The present invention satisfies these and other needs.
The present invention is directed generally to an endovascular graft for vascular treatment and a method for manufacturing and using the graft. The graft generally has an inflatable tubular frame structure which can be configured to conform to the morphology of a patient""s vessel to be treated. The frame structure has a proximal end and a distal end with an inflatable cuff disposed on at least one end and preferably both. The inflatable cuffs can-be reduced in diameter and profile when deflated for introduction into a patient""s vasculature by a catheter based delivery system or other suitable means. The inflatable cuffs provide a sufficiently rigid structure when inflated which supports the graft and seals the graft against the interior surface of the vessel in which it is being deployed. One or more elongated inflatable channels may also be disposed on the graft. Preferably, the elongated channel is disposed between and in fluid communication with a proximal and distal inflatable cuff. The channel provides the desired stiffness upon inflation, prevents kinking of the graft frame, and facilitates deployment of the graft within a patient""s body passageway. The elongated inflatable channel can be in a longitudinal or linear configuration with respect to the graft, but is preferably shaped as a helix disposed about the graft. Other orientations such as interconnecting grids or rings may also be suitable for the elongated channels. The inflatable cuffs and the elongated channel contain fluid tight chambers which are generally in fluid communication with each other but which may also be separated by valves or rupture discs therein to selectively control the sequence of inflation or deployment. The fluid tight chambers are typically accessed by an injection port which is configured to accept a pressurized source of gas, fluid, particles, gel or combination thereof and which is in fluid communication with at least one of the fluid tight chambers. A fluid which sets, hardens or gels over time can also be used. The number of elongated channels can vary with the specific configuration of the graft as adapted to a given indication, but generally, the number of channels ranges from 1 to 25, preferably 2 to about 8.
A proximal neck portion may be secured to the proximal inflatable cuff. The proximal neck portion has a flexible tubular structure that has a diameter similar to the proximal inflatable cuff. The proximal neck portion can be configured as a straight tubular section or can be tapered distally or proximally to an increased or decreased diameter. Preferably, the proximal neck portion is secured and sealed to the proximal inflatable cuff and tapers proximally to an increased diameter so as to engage the inside surface of a vessel wall which provides a sealing function in addition to that of the proximal inflatable cuff. Such a configuration also smoothes the transition for fluid flow from the vessel of a patient to the lumen or channel within the endovascular graft. The proximal neck portion has an inlet axis that preferably has an angular bias with respect to a longitudinal axis of the graft.
Preferably, the graft has a monolithic structure wherein the material that comprises the inflatable cuffs and channels extends between these elements in a thin flexible layer that defines a longitudinal lumen to confine a flow of blood or other fluid therethrough. Such a monolithic structure can be made from a variety of suitable polymers including PVC, polyurethane, polyethylene and fluoropolymers such as TFE, PTFE and ePTFE. Additional stiffness or reinforcement can be added to the graft by the addition of metal or plastic inserts or battens to the graft, which can also facilitate positioning and deployment of the graft prior to inflation of an inflatable portion of the graft.
In another embodiment, the graft has a thin flexible layer disposed over or between a proximal inflatable cuff, a distal inflatable cuff, and an elongated inflatable channel of the frame. The thin flexible layer is made of a material differing from the material of the cuffs or elongated channel. The barrier is shaped so as to form a tubular structure defining a longitudinal lumen or channel to confine a flow of blood therethrough. The flexible barrier may be made of a variety of suitable materials such as DACRON(copyright), NYLON(copyright), or fluoropolymers such as TEFLON(copyright) or the like.
An endovascular graft having features of the invention may be made in a tubular configuration of a flexible layer material such as Dacron, Nylon or fluoropolymers as discussed above. The inflatable cuffs and elongated channels are formed separately and bonded thereto. The inflatable cuffs and channels may also be made from the same layer material, i.e., Dacron, Teflon, or Nylon with a fluid impermeable membrane or bladder disposed within the cuff or channel so as to make it fluid tight. To limit permeability, the material in the regions of the cuffs and channels may also be treated with a coating or otherwise be processed by methods such as thermo-mechanical compaction.
In one embodiment of the invention, an expansion member is attached to the proximal end of the frame structure of the graft or to a proximal neck portion of the graft. Expansion members may also be attached to the distal end of the graft. Preferably, the expansion member is made of an expandable ring or linked expandable rings of pseudoelastic shape memory alloy which is self expanding and helps to mechanically anchor the proximal end of the graft to a body channel to prevent axial displacement of the graft once it is deployed. By having an expansion member which is distinct from the proximal cuff, the sealing function of the cuff, which requires supple conformation to the vessel wall without excessive radial force, can be separated from the anchoring function of the expansion member, which can require significant radial force. This allows each function to be optimized without compromising the function of the other. It also allows the anchoring function which can require more radial force on the vessel wall to be located more proximal from the aneurysm than the cuff, and therefor be positioned in a healthier portion of the vessel which is better able to withstand the radial force required for the anchoring function. In addition, the cuff and expansion members can be separated spatially in a longitudinal direction with the graft in a collapsed state for delivery which allows for a lower more flexible profile for percutaneous delivery. Such a configuration makes a collapsed delivery profile of 12-16 French possible, preferably below 12 French.
The expandable ring or rings of the expansion member may be formed in a continuous loop having a serpentine or zig-zag pattern along a circumference of the loop. Any other similar configuration could be used that would allow radial expansion of the ring. The expansion member may be made of suitable high strength metals such as stainless steel, Nitinol or other shape memory alloys, or other suitable high strength composites or polymers. The expansion member may be made from high memory materials such as Nitinol or low memory materials such as stainless steel depending on the configuration of the endovascular graft, the morphology of the deployment site, and the mode of delivery and deployment of the graft.
The expansion member preferably has an inlet axis which forms an inlet axis angle in relation to a longitudinal axis of the graft. The angled inlet axis allows the graft to better conform to the morphology of a patient""s vasculature in patients who have an angulated neck aneurysm morphology. The inlet axis angle can be from about 0 to about 90 degrees, preferably about 20 degrees to about. 30 degrees. Some or all of the inlet axis angle can be achieved in a proximal neck portion of the graft, to which the expansion member may be attached. An expansion member or members may also be attached to the distal end of the graft.
In another embodiment of the invention, the graft may be bifurcated at the distal end of a main body portion of the graft and have at least two bifurcated portions with longitudinal lumens in fluid communication with a longitudinal lumen of the main body portion. The first bifurcated portion and second bifurcated portion can be formed from a structure similar to that of the main body portion with optional inflatable cuffs at either the proximal or distal end. One or more elongated channels can be disposed between the inflatable cuffs.
The size and angular orientation of the bifurcated portions can vary, however, they are generally configured to have an outer diameter that is compatible with the inner diameter of a patient""s iliac arteries. The bifurcated portions can also be adapted to use in a patient""s renal arteries or other suitable indication. The distal ends of the bifurcated portions may also have expansion members attached thereto in order to anchor or expand, or both anchor and expand said distal ends within the body passageway being treated. The expansion members for the distal ends of the bifurcated portions can have similar structure to the expansion member attached to the proximal end or proximal neck portion of the main body portion. The expansion members are preferably made from a shape memory material such as Nitinol.
In bifurcated embodiments of grafts having features of the invention which also have a biased proximal end which forms an inlet axis angle, the direction of the bias or angulation can be important with regard to achieving a proper fit between the graft and the morphology of the deployment site. Generally, the angular bias of the proximal end of the graft, proximal neck portion or proximal expansion member can be in any direction. Preferably, the angular bias is in a direction normal to a plane defined by a longitudinal axis of the main body portion, the first bifurcated portion and the second bifurcated portion.
In another embodiment of the invention, rupture discs or other temporary closures are placed between fluid tight chambers of the inflatable cuffs and elongated channel or channels of the graft and form a seal between the chambers. The rupture discs may be burst or broken if sufficient force or pressure is exerted on one side of a disc or temporary closure. Once the graft is located at the site to be treated within a body passageway of a patient, a pressurized gas, fluid or gel may be injected by an inflation catheter into one of the fluid tight chambers of the graft through an injection port. Injection of a pressurized substance into an inflatable cuff will cause the cuff to take a generally annular shape, although the cuff can conform to the shape of the vessel within which it is deployed, and exert a sufficient radial force outward against the inner surface of the body passageway to be treated in order to provide the desired sealing function.
Multiple rupture discs can be disposed in various locations of the graft and also be configured to rupture at different pressures or burst thresholds to facilitate deployment of the graft within a body passageway. In a particular bifurcated embodiment of the invention, the proximal inflatable cuff of the main body portion may be positioned proximal of a junction between the branch of the abdominal aorta and the iliac arteries of a patient. As the proximal cuff is deployed by injection of an appropriate substance into an injection port in fluid communication with the fluid tight chamber thereof, it will expand radially and become axially and sealingly fixed proximal to the bifurcation of the aorta. A rupture disc is located between the fluid tight chamber of the proximal cuff and the elongated inflatable channels so that the proximal cuff may be substantially deployed before the rupture disc bursts and the elongated channels begin to fill with the injected substance. The elongated channels then fill and become sufficiently rigid and expand to create a longitudinal lumen therein. As pressure is increased within the fluid tight chamber, a rupture disc between the fluid tight chamber of the elongated channels and a fluid tight chamber of the optional distal inflatable cuff or distal manifold of the main body portion will burst and the distal inflatable cuff or manifold will deploy and become pressurized. One of the bifurcated portions of the graft may then be deployed as a rupture disc sealing its fluid tight chamber from the distal inflatable cuff or manifold of the main body portion of the graft bursts as the inflation pressure is increased. Finally, the second bifurcated portion of the graft deploys after a rupture disc sealing its fluid tight chamber from the main body portion bursts.
An inflation catheter which is attached to and in fluid communication with the fluid tight chambers of the graft via an injection port disposed thereon, can be decoupled from the injection port after completion of inflation by elevating pressure above a predetermined level. The elevated pressure causes a break in a connection with the injection port by triggering a disconnect mechanism. Alternatively, the inflation catheter can be unscrewed from its connection. The injection port can include a check valve, seal or plug to close off the egress of inflation material once the inflation catheter has been decoupled. The injection port could also be glued or twisted to seal it off.
A graft having features of the invention may also be deployed by percutaneous delivery with a catheter based system which has an inflatable balloon member disposed within expansion members of the graft in a collapsed state. The graft is percutaneously delivered to a desired site. Once the graft is axially positioned, the inflatable member of the balloon may be expanded and the expansion members forced radially against the interior surface of a body channel within which it is disposed. The expansion members may also be self expanding from a constrained configuration once the constraint is removed. After the graft has been positioned by the catheter system, the inflatable cuff or cuffs and elongated channel or channels of the graft are pressurized.
These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings.